One method of connecting a semiconductor die to a substrate such as a package substrate is through a soldered connection between a contact pad of the die and a contact pad of the substrate (e.g., a package substrate). An underfill material of, for example, an epoxy resin may be disposed around the soldered connection to improve, among other things, temperature cycling capability. One technique for introducing an underfill material is to introduce it to the die at the wafer level (i.e., before dicing of the wafer into individual dice). A typical process includes applying an underfill material as a blanket over a wafer surface including over contacts. The underfill material is then baked/cured and then planarized to a plane of the contact pads to expose the contact pads. A photoresist is then introduced and patterned leaving the contact pads exposed. This is followed by the application of a soldered paste to the contact pads and reflow to establish the solder connection to the individual contact pads. The photoresist material is then removed leaving the solder on the contact pads and the underfill material surrounding the contact pads.
To expose the contact pads through underfill material, current methods involve grinding, chemical mechanical polish or fly cut techniques. These methods produce residues that can embed in the underfill material between pads and potentially damaged fragile dielectric materials on the die. In addition, the current techniques to remove photoresist material from the wafer after solder reflow use wet (aqueous or organic) strippers. These strippers have a tendency to etch the backside of the wafer, solder and other film material. Photoresist materials are difficult to remove using conventional strippers because they generally have a high density of cross-linking to withstand a solder reflow temperature (e.g., 260° C.) and be compatible with a solder paste material and other processing materials. The more cured the photoresist material, the more cross-linking and the more difficult it is to remove without damaging other materials on the wafer. The temperature associated with solder reflow often contributes to the curing of the photoresist material.